One of the storage devices that may substitute a hard disk drive (HDD) is a solid state drive (SSD). The solid state drive has a garbage collection function to delete unnecessary data. In the solid state drive, the I/O (Input/Output) processing speed decreases once the garbage collection function starts up.
See, for example, Japanese Laid-open Patent Publication No. 2012-141944, Japanese Laid-open Patent Publication No. 2012-8651, and Japanese Laid-open Patent Publication No. 2011-192240.
The start-up timing of the garbage collection function depends on the firmware mounted in a solid state drive, and is unable to be controlled from the firmware of a disk array device (storage device) having the solid state drive mounted thereon.
For example, upon receipt of an I/O request with respect to a RAID (Redundant Array of Independent Disk) group from a host, the disk array device performs control to schedule write-back. A decrease in the I/O processing speed, i.e., an overload state, of one of the solid state drives constituting the RAID group results in a processing delay of the RAID group.
Such a processing delay of the RAID group disturbs the schedule of write-back and degrades the performance of the storage device.